High frequency oscillator



Aug. T18, 1936.

E. LANGMUIR HIGH FREQUENCY oscLLAToR` Filed March 28, 1954 ANOE PLASMA[ON/ZAELE MED/UM PLASMA i;

help? inventor:

.m U m w ma m a@ Lf A mW/S v i rJH l y b Patented Aug. 18, 1936 'HIGHFREQUENCY OSCILLATOR Irving Langmuir, Schenectady, N. Y., assignor toGeneral Electric Company, a corporation of New York Application March28,

Claims.

My invention relates to high and ultra-high frequency oscillators andmore particularly to such oscillators utilizing electric dischargedevices containing an ionizable medium.

5 Heretofore, there have been devised numerous circuit arrangementsutilizing electric discharge devices for generating electricaloscillations of a frequency suitable for communication, particularlyradio. Perhaps one of the best known and most widely used type ofoscillators is that comprising a high vacuum, pure electron dischargedevice. In this type of oscillator the instantaneous increase of thedischarge device varies directly with the instantaneous value ofthe gridpotential, so that, by proper interaction between the grid circuit andthe output circuit, oscillations are generated of a frequency dependentupon the tuning of one of said circuits, as is well understood by thoseskilled in the art. This type of oscillator is very stable in operation,but is subject to the disadvantage of a relatively low eiliciency due tothe large resistance losses in the discharge device. Therefore, it hasbeen difficult to build oscillators of this type which would produceefliciently a relatively high power output.

Other types of oscillators are known to the art, such as those utilizinga cold cathode vapor electric discharge device, and the type known as aninverter. The former has the disadvantage that it is diflicult tocontrol accurately the frequency of the generated oscillations and thelatter in its present commercial form is limited in its utility by thefact that the deionization time of the dis- .charge device is of suchmagnitude that high frequency oscillations suitable for communicationpurposes, are not now obtainable.

I have discovered the following phenomenon to be present in anelectrical discharge device comprising an envelope containing anionizable medium at a pressure which is sumcient to permit ionization ofsuch degree as to form a plasma, but yet not great enough to impedeseriously the free motion of electrons. A plasma is generally defined inthe art as being an electrically neutral body composed of an ionizedmedium. These ionizable media may comprise mercury vapor at a relativelylow pressure, in which case the pressure would preferably lie within therange of 0.1 to 2 microns. or one of the 'rarer gases such as argon,helium, or neon. For comparable operation the helium and neon gases areat a pressure of about a millimeter of mercury. If we have an electricdischarge device comprising an envelope containing at'one extremity ananode and a cathode, and at the opposite extremity an anode 1934, SerialNo. 717,747

(Cl. Z50-36) and a cathode, and a single grid structure locatedintermediate the groups of anodes and cathodes, and introduce anionizable medium into the envelope of the proper pressure, it will bepossible to set up within this tube a plurality of 5 plasmas. If we nowassume that plasmas have been formed about each group of anodes andcathodes and furthermore that the grid element is suiciently large toseparate the envelope into compartments, a negative charge placed upon10 the grid will cause the grid to be surrounded by a positive ionsheath which will completely isolate the plasmas from each other. Thethickness of the positive ion sheath is dependent upon the cathodetemperature, the anode voltage and l5 the charge upon the grid. If thecharge or voltage on the grid is varied rapidly, the thickness of thepositive ion sheath follows these variations practicallyinstantaneously. If the voltage on the grid is varied sufficiently, thethickness of the 20 positive ion sheath may be reduced to such magnitudethat there may be an interchange or flow of electrons between the twoplasmas.

In accordance with my invention, I utilize the above phenomenon in theconstruction and opera- 25 tion of an oscillator having a double plasmaelectric discharge device. In the preferred embodiment, this doubleplasma discharge device comprises an envelope containing an anode, acathode, a grid element and an ionizable medium, 30 such as one of therarer gases, or mercury vapor at a relatively low pressure. The gridelement, which is located between the anode and the cathode, is ofsuflicient magnitude or is of such configuration that the grid elementwill completely separate the anode plasma from the cathode plasma. Thismay be accomplished in a number of different ways, one of which may beto construct the grid of uniform mesh which extends to the sides of theenvelopes, thus separating the envelope into two compartments. If nowpositive potentials are applied to the grid and to the anode and thecathode is energized, ionization will occur. If now a momentary negativecharge is placed upon the grid, the ionized 45 medium will be dividedinto anode and cathode plasmas by the positive ion sheath which formsabout the grid. Thus. one compartment contains the anode plasma and theother compartment contains the cathode plasma. This positive ion 50sheath is substantially continuous and it is capable of preventing orinterrupting an electronI iiow between the two plasmas without thenecessity oi deionization of the ionizable medium. If

this momentary negative charge upon the grid is succeeded by a periodicvariation which tends to cause the grid to become more positive or tocause a variation in the potential difference between the plasmas, thepositive ion sheath edges move back and forth during each variation ofthe grid potential so that during a portion of each cycle the edge ofone side of the sheath moves up to the immediate proximity of the grid.At this tlme, the electrons from one plasma will pass through the gridto the other plasma. The control effect of the grid element does notchange the electron ow directly with the instantaneous value of the gridpotential, as in the high vacuum type electron discharge device, but itis rather an on and od eect so that the full electron. flow is eitherpresent or not present, depending upon whether the grid voltage is aboveor below a certain value. This critical value of the grid voltagedepends upon the nature of the ionizable medium within the envelope.Thus, in some instances the charge upon the grid is `negative withrespect to the cathode and in other instances is negative with respectto the anode potential. This double plasma discharge device has theadvantage that there are no large resistance losses, as in the highvacuum type device, as this device operates during the peak ofalternating potentials on the grid element with an electron :dow whichis limited principally only by the cathode emission.

In the lelectric discharge devices containing an ionizable mediumcommonly in. use today, such as devices known in the art under thetrade-mark Thyratrons, the ow of current through the device isdetermined by the variation of the ionization of the ionizable medium.In such devices the degree of ionization varies from the time of theinitiation of the discharge until the discharge is completed and duringthe time of nonconductivity the discharge device is in a deionized.state. in the double plasma discharge device the ionization or theconcentration of ions remains substantially constant and the changes inthe anode current during each cycle resulting from the variations in thethickness of the positive ion sheath about the grid are due to adisplacement of the electrons but not to a dow of ions or change ofionization intensity.

For this reason the double plasma tube can operate to repeat at the highfrequencies at which pure electron (or gas free) discharge devices canoperate and it is not restricted to the lower frequencies usuallycharacteristic of devices operating with an ionized medium.

It is an object of my invention, therefore, to utilize such a doubleplasma electric discharge device in high and ultra-high frequencyapparatus.

t is another object of my invention to provide an improved oscillatorwhich will overcome some of the disadvantages of the arrangements of theprior art, and which will be simple, reliable, and powerful inoperation. 4

It is a further object of my invention to provide an improved oscillatorutilizing an electric discharge device containing an ionizable mediumwhich will generate powerful oscillations of high and ultra-highfrequency.

The novel features which i believe to be characteristic of my inventionare set forth in particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further ob- Ajects and advantages thereof, will be betterunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Fig. 1 discloses an apparatusutilizing one of the tubes described in my invention, and Fig. 2discloses the preferred form of the double plasma electric dischargedevice suitable for operation as an oscillator.

Referring to Fig. 1 of the drawing, I have illustrated therein anoscillation generator utilizing an electric discharge device comprisingan envelope I0 which is filled with an ionizable medium at a pressurejust sumcient to permit an ionization necessary to allow plasmaformation yet not of sufficient pressure so as to impede materially orseriously the free motion of electrons. This ionizable medium maycomprise mercury vapor at a relatively low pressure or one of the rarergases such as argon, helium, or neon. The envelope contains the anodeii, the auxiliary anode il', acathode i2 and a grid element i3. The gridelement, which should be of such configuration or magnitude as toseparate adequately the anode plasma from the cathode plasma, is in thisinstance disclosed as a uniform mesh member which extends to the wallsof the discharge device. The cathode i2 is energized from a suitablesource of potential itl and the anode potential is supplied by a sourceof potential l5. The anode il is connected tothe source of potential i5through a lead which includes a choke coil i6 which serves to preventthe high frequency from passing through the sources of potential it andi5. The anode to cathode circuit of the anode i l, comprises thefollowing elements: A capacitor il, an inductor i8, a lead i9, acapacitor 23, a lead 2i and a capacitor 22. The grid-to-cathode circuitcomprises the following elements: The inductor 23 which is coupled tothe anode inductor i8, the lead i9, capacitor lead 2i and capacitor 22.A variable capacitor 2f@ connected across the inductors i8 and 23 servesto operate as a tuning means for determining the resonant frequency ofthe anode and grid circuits. inasmuch as the operation of thearrangement is not dependent in any way upon the time of deionizatiou ofthe discharge device, the oscillation period of these circuits may be ofa lower order of magnitude than that of the period of deionization ofthe discharge device. In order to insure the existence of a cathodeplasma the anode ii is connected through the lead 2i and a tap 25 to thesource of potential id.

Due to the fact that the capacitor 2@ is connected through the tap 25 toa source of positive potential, a portion of the battery l5, the lowerside of the capacitor 2li is positively charged y and consequently theupper side of the capacitor has a negative charge. This negative chargeis impressed upon the grid i3 thus producing about the grid a positiveion charge. The positive ion charge surrounds each of the individualwires of the grid mesh and if the potential on the grid and the wiresVare properly proportioned this positive ion charge or sheath will form asubstantially continuous layer which normally isimperv'lous to the flowof electrons from the cathode plasma to the anode plasma. A portion ofthe energy in the high frequency anode circuit is transferred to thegrid circuit due to thecoupling between the inductors I8 and 23. Thistransfer of energy from the anode circuit to the grid circuit causes thenegative charge upon the grid I3 to be varied and causes a variation ofthe potential diierence between the plasmas. As the charge on the gridis varied the edges of the positive ion sheath move back and forthduring each cycle so that during a small portion of each cycle the edgeat one side of the sheath moves up to the immediate proximity of thegrid I3. At this time the electrons from one plasma pass through thegrid to the other plasma. Thus, there is a iiowht electrons from oneplasma to the other during the peak of each cycle of the voltagevariation on the grid I3, which iiow is limited principally by thecathode emission.

While I do not wish to be limited thereto, I believe that the aboveexplanation presents the true theory of the operation of the doubleplasma electric discharge device as an electric high frequencyoscillator.

Reference may now be had to Fig. 2 wherein I have disclosed thepreferred embodiment of the double plasma electric discharge device.This figure also shows in detail the manner of supporting and arrangingthe grid in the envelope of the discharge device so as to separate theanode plasma from the cathode plasma. The device shown in this iigurecomprises a cylindrical envelope I0 supporting at one end the anode IIand at the opposite end the cathode I2. The

grid element should be of such configuration that the cathode plasmawill be separated from the anode plasma by the positive ion sheathformed about the grid. One form of grid which will suffice may be acylindrical grid preferably of a` lesser diameter than said envelope,closed at one end and located so as to enclose substantially either thecathode or the anode. Another form of the grid may be like thatdisclosed in the present example where the grid is supported by asecondary glass wall 26 which ls arranged so that only the uniform meshof the grid I3 is exposed to the ionizable medium contained within theenvelope I0. An advantage gained by supporting the grid element by thesecondary glass wall 2G is that no metallic supporting structure of thegrid is subject to the ion bombardment commonly known as sputtering. Byplacing the proper potential upon the grid I3 a positive ion sheath ofsubstantially uniform thickness will form and serve to separate theionizable medium into anode and cathode plasmas. It will be noted thatthe discharge device disclosed in Fig. 2 does not have the auxiliaryanode II which is disclosed in Fig. l, as it has been found that undercertain conditions this auxiliary anode may be dispensed with.

It is to be understood that while I have shown a means for supplying anegative charge upon the grid I3 in Fig. 1 as a capacitor, that anyother means may be substituted, such as a bias battery. Also any otherform of transferring a portion of the energy in the anode circuit of thedischarge device to the grid circuit may be utilized, such as capacitivecoupling. Furthermore,

. the circuit arrangement 4disclosed is merely exemplary of one of anumber of circuits which may'be utilized with the double plasma electricdischarge device for the generation and reproduction of high andultra-high frequency oscillations.

The oscillation generator disclosed and described herein is capable ofgenerating oscillations of 300,000 kilocycles or more.

Due to the fact that current is passed from one plasma to the otherduring each positive mak of the cycle of the voltage alternationsimpressed upon the grid, the apparatus operates at a, relatively higheiiciency because there are no large resistance losses in the dischargedevice. This apparatus, therefore, has the advantage that it may be usedas a power oscillator at high or ultra-high frequency.

While I have shown and described my invention in connection with certainspecific embodiments, it will, of course, be understood that I do notwish to be limited thereto, since it is apparent that the principlesherein disclosed are susceptible of numerous other applications, andmodifications may be made in the circuit arrangement and in theinstrumentalities employed without departing from the spirit and scopeof my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: A

1. A high frequency apparatus including a discharge device comprising anenvelope containing an ionizable medium at a pressure sufficient topermit ionization without material impediment to free electron movement,an anode, a cathode and a controlv grid element included within saidenvelope, said control grid being arranged to separate said envelopeinto anode and cathode compartments, means connected to said anode andsaid cathode for producing ionization of said medium, and meansincluding said control grid for controlling the interchange of electronsbetween said compartments without substantial variation of the degree ofionization of said ionizable medium.

2. A high frequency apparatus including a discharge device comprising anenvelope containing an ionizable medium at a pressure sufficient topermit -ionization without material impediment to free electronmovement, an anode, a cathode and a control grid element included withinsaidl envelope, said control grid being arranged to separate saidenvelope into anode and cathode compartments, means connected betweensaid anode and said cathode for producing ionization of said medium, andmeans for varying an electrical condition of said grid in a manner tocontrol the interchange of electrons between said compartments withoutsubstantial variation of the degree of ionization of said ionizablemedium.

3. A high frequency apparatus including a discharge device comprising anenvelope containing an ionizable medium at a pressure sufcient to permitionization without material impediment to free electron movement, ananode, a cathode and a control grid element includedwithin saidenvelope, said control grid element being arranged to separate saidenvelope into anode and cathode compartments, means for producingnormally about said control grid element av substantially continuouspositive ion sheath, and means forvarying the condition of said positiveion sheath in a manner to control the flow of electrons between saidcompartments without substantial variation of the degree of ionizationof said ionizable medium.

4. A high frequency apparatus including a disi charge device comprisingan envelope containing an ionizable medium at a pressure suicient topermit ionization without material impediment to electron movement, Aananode, a cathode and a grid element included within said envelope, saidgrid being suiiicient in magnitude and coniiguration to separate saidenvelope into anode and cathode compartments, a source of potentialconnected 4between said anode and said cathode, means for impressing apotential upon said grid with respect to other elements of said deviceto produce normally a substantially continuous positive ion sheathbetween said'compartments, a grid-cathode circuit and an anode-cathodecircuit for said discharge device, and means for impressing highfrequency energy upon said gridcathode circuit for reproduction in saidanodecathode circuit. l

5. A high frequency oscillator including a discharge device comprisingan envelope containing an ionizable medium at a pressure sukcient topermit ionization without material impediment to electron movement, ananode, a cathode and a grid element included within said envelope, saidgrid being suiiilcient in configuration to separate said envelope intoanode and cathode compartments, a source of potential connected betweensaidanode and said cathode, means including a potential impressed uponsaid grid with respect to other elements of said device to producenormally a substantially continuous positive ion sheath between saidcompartments, a gridcathode circuit and an anode-cathode circuit forsaid discharge device, and means for transferring a portion of theenergy present in said anode-cathode circuit to said grid-cathodecircuit.

6. A high frequency oscillator including ,a discharge device comprisingan envelope containing an ionizable medium at a pressure sulcient topermit ionization without material impediment to electron movement, ananode, a cathode and a grid all included within said envelope, said gridbeing located between said anode and said cathode and of suchconfiguration as to separate said envelope into anode and cathodecompartments, a source of potential connected between said anode andsaid cathode, means for impressing a potential upon said grid withrespect to other elements of said device sufficient to produce normallya substantially continuous positive ion sheath about said grid, a gridcircuit connected between said grid and said cathode, an output circuitconnected between said anode and said cathode, and means for impressinga portion of the energy present in said output circuit upon said gridcircuit.

7. A high frequency oscillator including a discharge device comprisingan envelope containing an ionizable medium at a pressure suihcient topermit ionization without material impediment to electron movement, ananode, a grid and a cathode included within said envelope, said gridseparating said envelope into anode and cathode compartments, a sourceof potential connected between said anode and said cathode, means forimpressing a potential upon said grid with respect to other elements ofsaid device to produce normally a substantially continuous positive ionsheath around said grid, said sheath separating said ionizable mediuminto anode and cathode plasmas, a circuit connected between said gridand said cathode, a circuit connected between said anode and saidcathode, and means for transferring a portion of theanode circuit energyto said grid circuit whereby said positive ion sheath will besufliciently altered to permit electrons to pass from one plasmato theother thereby producing high frequency oscillations.

8. A high frequency oscillator including a discharge device comprisingan ionizable medium at a pressure sufiicient to permit ionizationwithoutmaterial impediment to electron movement, an anode, a cathode anda grid element included within said envelope, a source of potentialconnected between said anode and said cathode, said grid element beingof sufficient magnitude and conguration to separate said medium intoanode and cathode plasmas, means for impressing a potential upon saidgrid with respect to other elements of said device to produce normally asubstantially continuous positive ion sheath about said grid, a grid tocathode plasma circuit and an anode plasma to cathode plasma circuit forsaid discharge device, means for transferring a portion of said secondcircuit energy to said first circuit, and means for tuning at least oneof vsaid circuits to an oscillation period of a lower order of magnitudethan the deionization time of said discharge device.

9. A high frequency oscillator including a discharge device comprisinganode, cathode and grid elements enclosed within' an envelope containingan ionizable medium at a pressure sufcient to permit ionization withoutmaterial impediment to electron movement, means including a source ofpotential connected between said anode and said cathode for producingplasmas, plasmas surrounding each of said anode and cathode elements,means for producing normally a positive ion sheath about said grid toseparate said anode and cathode plasmas thereby normally restricting theow of electrons between said plasmas, grid to vcathode plasma and anodeplasma to cathode plasma circuits for said discharge device, means fortuning at least one of said circuits, and means for transferring aportion of theanode-cathode circuit energy to said grid circuit wherebysaid positive ion sheath will be altered periodically to vary the flowof electrons between said plasmas.

10. A high frequency oscillator including a discharge device comprisinganode, cathode and grid elements enclosed within an envelope containingan ionizable medium at a pressuresuflicient to permit ionization withoutmaterial impediment to electron movement,mea ns including a source ofpotential connected between said anode and said cathode for producingplasmas, plasmas surrounding each of said cathode. and anode elements,means for producing normally a substantially continuous positive ionsheath about said grid to separate said plasmas and to normally restrictthe flow of electrons between said plasmas, an anode-cathode circuitincluding a source of potential tending to cause a flow of electronsbetween said plasmas, a grid-cathode circuit for saiddischarge device,means for tuning at least one of said circuits, and means fortransferring a portion of the energy of said anode-cathode circuit tosaidgrid-cathode circuit whereby said G0 positive ion sheath and thepotential difference between said plasmas will be altered sufficientlyto produce a periodic flow of electrons between said plasmas.

IRVING LANGMUIR.'

